Romans 14:16-20 meaning

Using Paul's example of food and drink, even if a believer with stronger faith believes that it is okay to consume a certain food or drink, he shouldn't partake of that substance among Christians with weak faith. Paul has defined someone as having weak faith if their conscience is violated by something that is optional. 

If those with strong faith flaunt their freedom around weak believers, they may cause them to do things that violate their conscience. In doing this, it leads them to sin (Romans 14:23; 1 Timothy 1:19). 

Believers should pursue righteousness (right and harmonious living) with one another rather than arguing over opinions (v 1). Paul seems to be primarily concerned with substances, food, and drink in this chapter, but he appears now to broaden to a general principle to make sure to declare that the kingdom of God is not about earthly preferences, and so those with strong faith should bear in mind the conscience of others: Therefore do not let what is for you a good thing be spoken of as evil (v 16). 

This might be a primary reason Paul continued to live consistent with Jewish tradition throughout his life (Acts 28:17). He might have done so because he desired to maintain his witness with them, and keep from creating a stumbling block (1 Corinthians 9:22; Acts 16:3). 

There are many activities that can be harmless, but some Christians' consciences or walk with God are negatively influenced by them. In a church setting, our goal is to build each other up, not to cause problems and arguments over earthly substances, for the kingdom of God is not eating and drinking, but righteousness and peace and joy in the Holy Spirit (v 17). 

As believers, even if we think something is fine to eat or drink, we should abstain from it when around other believers who look at it as sin, as something that is evil: For he who in this way serves Christ is acceptable to God and approved by men (v 18). 

That does not necessarily mean that we must personally give up things we enjoy that do not cause us to sin, but we should be mindful of how our freedoms affect other Christians' faith, specifically those who have weak faith. This is because we are to serve each other with humility (Romans 12:3), sacrificing for one another. 

So then we pursue the things which make for peace and the building up of one another (v 19). Fellow believers matter more than earthly substances. Our focus should be on benefitting others above our own comfort or enjoyment. 

In living harmoniously with each other, sacrificing for one another, we are serving Christ—which is the kind of service that is acceptable to God and approved by men. In abstaining from petty arguments about consuming substances that hurt another believer's conscience, we will create peace and build each other up. In this way we pursue harmonious living.

Paul then speaks of our fellow believers as a work of God. He exhorts: Do not tear down the work of God for the sake of food (v 20). When we become a stumbling block to a fellow believer and cause them to sin, we tear down God's work, because each believer is a new creation in Christ (2 Corinthians 5:17). 

We might say "But there is nothing wrong with what I am doing." Perhaps so. Paul asserts, All things indeed are clean. God made everything, and everything is good, when done according to God's design. But anything that is applied against God's design is harmful. And to violate the conscience is harmful. So, although all things are clean, Paul says: but they are evil for the man who eats and gives offense (v 20). 

These good things are evil because they violate the conscience. And anything that violates our conscience is sin (Romans 14:23). 

Paul ends this section by stating that even though all food and drink is clean and okay for believers to consume, we should not eat those substances around believers whose consciences believe that such consumption is wrong— this is because righteous, harmonious living is what God wants from us, and arguing over these things will prevent that.

Paul here deals with food and drink, but this principle applies to anything that would wound the conscience of another.